Field of the Invention
The present invention relates to a device for contacting and/or electrostimulation of biological tissue, preferably a retina, by means of at least one electrode, wherein the device has at least a first unit, on which the at least one electrode is provided and which is configured for implantation in a human or animal body, a second unit, which provides a voltage supply for supplying the first unit with electrical energy, and at least a first and a second conductive track for connecting the voltage supply to the first unit, the conductive tracks respectively being electrically connected to the first unit and second unit and being at different voltage potentials.
Related Prior Art
Such devices are widely known from the prior art.
The first unit, configured as an implant, is used for example as a retinal implant for stimulation of nerve cells in the eye, as a cochlear implant for stimulation of the human inner ear, as a neural implant for stimulation or tapping of electrical signals from regions of the brain, or very generally for stimulation or tapping of electrical signals of biological tissue.
The implants must in this case respectively be supplied with electrical energy, to which end they are connected to a supply unit forming a second unit, which is likewise implanted or arranged outside the body. Provided between the two units, there are current-carrying conductive tracks consisting of noble metals such as gold, platinum or titanium, which are protected from bodily fluids by a plastic sleeve.
In the case of some implants, the connection between the first and second units is produced by means of wires in which electrical signals are transported and the electrical potentials of the supply voltage are provided. The wires are coated with a plastic insulator in order to avoid short circuits. Silicone is mostly used for this, so that the wires are not only insulated from one another but at the same time also provided with good mechanical protection. The silicone enclosing the wires has a thickness great enough to ensure sufficient protection even against the wet environment which is detrimental to electronics.
If, however, retinal implants or neural implants are intended to be provided with electrical energy, then the spatial conditions are very much narrower, because for example only little free space is available in the eye for placement of relatively thick cables.
For this reason, flexible connecting bands are used for the supply of retinal implants, which are configured in the manner of a narrow, elongate flexible printed circuit board. The conductive tracks are in this case embedded between two biocompatible plastic layers. Polyimides, Parylene, LCP (liquid crystal polymer) or silicones may be envisaged as materials for the plastic layers.
Such retinal implants are known for example from WO 2004/067088 A1, WO 2008/037363 A2 and DE 10 2006 021 258 A1, to the content of which reference is hereby expressly made.
The known retinal implants are implanted in the subretinal or epiretinal space of the eye, in which case the second unit may be formed on the same flexible substrate as the first unit, as described for example in DE 10 2006 021 258 A1.
The second unit may in this case contain an infrared receiver which converts incident IR light into electrical energy for supplying the first unit.
It is also known to form the first and second units onto two different substrates, to connect these two substrates to one another by means of a flexible connecting band and to implant both into the eye.
In other applications, the second unit is an external unit which is suitably fastened outside the body, for example on the forehead, as is known for example from WO 2008/037363 A2 or DE 10 2006 021 258 A1.
The external second unit and the implanted first unit are then likewise connected to one another by means of a flexible connecting band, which for example likewise extends in the subretinal space.
The external second unit configured as a supply unit may in this case draw electrical energy for the first unit formed as an implant from batteries, receive it via external cables or obtain it from electromagnetic energy, as is known for example in WO 00/67676 A1.
A feature common to the active retinal implants described above is that they have a multiplicity of stimulation electrodes which deliver electrical stimulation signals to retinal cells to be contacted. A multiplicity of pixel elements are furthermore provided, which convert incident light into the stimulation signals. For further details, reference is made to the documents cited above.
The described retinal implants have already proven themselves in medical terms, but their residence time in the eye is however still limited in technical terms because, after a residence time of less than 100 hours, short circuits or line interruptions occur between the two conductive tracks which connect the first and second units to one another for the purpose of the voltage supply, so that the voltage supply of the implant is no longer ensured and it must be explanted, or replaced.